California and 18 other USA states said on Thursday they would sue to stop a Trump administrationproposal to weaken Obama-era federal fuel efficiency standards, arguing the United States has an obligation to protect the environment for future generations. The 2020 standard would be around 32 miles per gallon.

But Andrew Wheeler, the acting chief of the EPA, told lawmakers on Wednesday that he doesn't want the federal standard to contradict states that want to require higher gas mileage. The administration also says that its preferred plan for fuel economy will reduce society-wide spending by $502 billion for vehicles built between 1975 and 2029.

Fuel efficiency is unsafe for drivers, the Trump administration claims.

"It's a proposal that attacks the states' right to protect people from unsafe pollution, one that no one -- not the American public, not the states, not even most automakers -- really wants, and one that's being presented to the public under the false and easily discredited guise of improving public safety", the statement continued.

Environmental groups are already expressing their outrage over the plan.

California's Democratic senators, Kamala D. Harris and Dianne Feinstein, introduced a nonbinding resolution Thursday with 32 other senators asserting California's authority to set its own tailpipe emissions standards and supporting the current "One National" program on emissions.

Environmental groups criticized the assertion about reducing crash deaths, and said the proposal would drive up gasoline prices, increase asthma-inducing smog, and reverse one of the most significant steps Washington has taken to curb climate-changing greenhouse gas emissions.

"It's my goal and this administration's goal to come up with a 50-state solution, and we want to have a 50-state solution that does not necessitate preempting California".

The administration said the freeze would boost US oil consumption by about 500,000 barrels of oil a day by the 2030s, and argued it would prevent up to 1,000 traffic fatalities per year by reducing the price of new vehicles and so prompting people to buy newer, safer vehicles more quickly.

California and 16 other states sued in the administration over the fuel efficiency standards in May, anticipating the new regulation.

Gina McCarthy, thes EPA administrator under Obama, said the reversal of these standards "run contrary to sound science and the law".

The administration must gather feedback on the proposal before it is finalized, a process that could take months and that could be further delayed by lawsuits. "This is a demolition, and there's no scientific or technological justification for it".